ATA disk arrays make an excellent target for off-site replication. Traditionally, replication is relatively high on the adoption curve. First, people make sure their data is being backed up. Then they make sure that it's protected against disasters by moving and backing it up off site. After that, most storage administrators begin to look at high-availability designs. Most high-availability systems are designed to get around individual component failure. They aren't usually designed to withstand a disaster that destroys the entire data center.
There are high-availability systems that now incorporate off-site replication, but they're extremely expensive. The cost of such a system is derived from four areas:
- The off-site data center
- The conductivity to the off-site data center
- The servers within the data center
- The storage connected to servers
Using colocation facilities, cheap servers and an ATA disk array, even the smallest business can afford to replicate their data off site. There's even free software replication products for Unix and Windows. A directory of these products is available here.
Remote site replication
It's also possible to use a large ATA disk array as a target for the replication of several remote sites. Today, the typical backup and recovery solution for several remote sites is to place an inexpensive tape drive and some type of backup and recovery software at that location. The problem with such a setup is that it's subject to human error. A recent customer of mine found that the backups of their 100+ remote offices failed more than 50% of the time simply because the managers of the remote offices failed to insert a tape.
Replicating remote offices' data to a central ATA disk array saves thousands of dollars in tape drives, backup software and people hours. Such a system is also more reliable than a system that relies on a person to insert a tape. Of course, you could also solve that problem by leaving the tape in the tape drive, overwriting last night's backup with tonight's backup. But you know that's not a smart protocol to follow.
Another use of ATA disks and colocation facilities is to use a disk-based backup and recovery system to back up your servers off site. As I first explained in "Pick the right ATA array for backup," a true disk-based backup and recovery system understands that it's backing up to disk and takes advantage of the medium's random access capabilities. This lets you store only one copy of each unique file or block of data--no matter how many times that file or block appears on your network's computers. It can also do block-level incremental backups that back up only the changed blocks of each file, and forego occasional full backups. Since all the backups are instantly accessible, restoring from hundreds of incremental backups--even block-level incremental backups--takes the same amount of time as restoring from a single full backup. In fact, it could be faster to read hundreds of smaller backups from many disks instead of reading one large backup from one disk.
This was first published in February 2003